Apparatus and method for handling volatile liquids

ABSTRACT

Hydrocarbon vapors normally released to the atmosphere during the filling of tanks with a relatively volatile liquid are condensed out and recovered as liquid by simultaneously compressing the vapors and saturating the same with vapors of the liquid, followed by a step wherein the compressor effluent is contacted under elevated pressures in a condensation column with a refrigerated stream of the volatile liquid. Said stream is supplied from a relatively small holding tank which is refrigerated and maintained at a relatively constant volume by addition of fresh quantities of the liquid as required.

O Umted States Patent 1 1 1 1 3,714,790

Battey 1451 Feb. 6, 1973 1541 APPARATUS AND METHOD FOR 2,765,872 10 1956Hartman ....220/85 VR HANDLING VOLATILE LIQUIDS 2,947,379 8/1960 Aubrey....220/85 VR 3,369,371 2/1968 Holly etal ..62/54 [75] Inventor: RobertF. Battey, Upland, Calif. I

[73] Assignee: FMC Corporation, San Jose, Calif. Primary Examiner-MeyerPeru Assistant ExaminerRonald C. Capossek [22] Flled: 1971 Attorney-F.W. Anderson and C. E. Tripp [21 A 1. No.: 133638 1 pp 57 ABSTRACT 52U.S. (:1. ..62/54, 55/88, 55/89, Hydmcarbc ,F 9"" T' 22O/85vR mosphereduring the filling of tanks with a relatively volatile li uid arecondensed out and recovered as 51 1111. C1 ..F17c 13/00 b h l th d [58]Field of Search ..62/54; 220/85 VR, 85 vs; y mpressmg 55/88 89saturating the same with vapors of the liquid, followed by a stepwherein the compressor effluent is contacted 56 R f d .under elevatedpressures in a condensation column 1 e erences v with a refrigeratedstream of the volatile liquid. Said UNITED STATES PATENTS stream issupplied from a relatively small holding tank which is refrlgerated andmamtamed at a relatively 3,266,262 8/1966 Moragne ..62/54 constantvolume by addition of fresh quantities of the 2,059,942 11/1936 Gibson..220/85 VR as re ui ed 2,379,215 6/1945 Brinkman.... ..220/ 8'5 VR q q1 2,849,150 8/1958 Tompkins ..220/85 VR 7 Claims, 1 Drawing Figure VENTCo/vmws/ar/m/ COLUMN 60 3/) if 1; ASOL/A/E STOP/ 65 E 43 42 SraavaE Inorder to recover condensable vapors from the gaseous stream which isdischarged from many tanks as the latter are filled with gasoline orother volatile liquids, resort has commonly been had to the form ofapparatus disclosed in U.S. Pat. Nos. 2,765,872 and 2,849,150, whereinthe vapors are first collected, then saturated with the liquid vapors toprovide a non-explosive mixture and collected under ambient pressures ina large gas-holding tank. The latter tank is sized to receive the vaporsat peak tank-loading rates and to discharge the same for processing at alower, more or less constant rate as gas pressures build up in the tank.The vapor stream so discharged is then compressed and absorbed underelevated pressures as it is contacted with the liquid fuel under ambienttemperatures in an absorption column. This gas-holding tank, which mustbe unusually large so as to receive at ambient pressures the vaporsdisplaced at peak rates during periods of tank loading, is a veryexpensive item of equipment, and it is an object of this invention toprovide a vapor recovery system which is relatively inexpensive andrequires no such vapor-holding tank in order to accommodate itself tothe processing of vapors as received at peak rates. A further object ofthe invention is to provide a method and means for preventing the escapeinto the atmosphere of condensable vapors discharged from tanks as theyare loaded with a volatile liquid and for recovering said vapors in theform of condensed liquid.

The nature of still further objects of the invention will be apparentfrom a consideration of the descriptive portion to follow.

SUMMARY OF THE INVENTION The present invention relates to a method forrecovering hydrocarbon vapors or those of other low boiling organiccompounds as said vapors are displaced from tanks during liquid-loadingoperations, thereby preventing escape of the vapors to the atmosphere.In carrying out-the method, vapors exiting from the tank are captured,then saturated and compressed followed by a condensation step whereinthe effluent from the compressor is contacted under elevated pressuresin a condensation column .with a quantity of the gasoline or othervolatile liquid being handled which enters said column inra refrigeratedcondition. The hydrocarbon or other low-boiling vapors present arecondensed as well as absorbed by the cold liquid during this contactingstep. The residual gaseous portion of the vapor stream recovered fromthe tank consists essentially of air and is discharged from thecondensation column to It is a feature of this invention to maintainwithin the system a relatively small reservoir of refrigerated liquid ofsubstantially the same composition as that being loaded into thereceiving tank, thereby permitting the installation and use ofrefrigeration equipment and of a cold liquid holding reservoir of modestsize and cost. The capacity-of this refrigerated liquid'reservoir issuchthat, under the pressure and temperature conditions prevailing inthe condensation column, vapors collected during an extended period ofpeak tank-loading operation can readily be processed and recovered usingthe reserve of refrigerated liquid maintained in the reservoir. Thismethod of operation proves to be far less costly, particularly from acapital investment standpoint, than is that wherein a largevapor-holding tank is incorporated in the system to receive vaporsduring said peak periods.

The invention can be clearly understood by reference to the appendeddrawing which is a diagrammatic illustration of a process flow suitablefor the practice of the invention in connection with the filling ofgasoline storage tanks or tank trucks. However, it is to be understoodthat the invention is adapted to be used in connection with othervolatile liquids which may be combustible or not. In the drawing, noattempt is made to indicate all the pumps, valves and other items ofcontrol equipment and the like since the location thereof can readily besupplied by those skilled in the art in the light of the presentteachings.

Referring to the drawing, gasoline from a primary storage tank 10 iswithdrawn through line 11 and pumped by pump 12 through line 13 to afiller hose 14. Said hose extends through a vapor collecting hood l5shaped to be fitted into the gasoline receiving opening of a truck orother receiving tank 16. The hood 15 has a vapor receiving line 20 whichextends from the hood to a flame arrestor 21 and thence to a compressor23 which operates only when gasoline is being loaded into tank 16. Alongwith the vapors, the compressor is supplied with a stream of coldgasoline through line 30, said gasoline being withdrawn from a coldgasoline storage reservoir 31 and supplied to line 30 through an outletline 32 and a pump 33 which runs when the compressor 23 is actuated. Asthe vapors pass through the compressor, they also become saturated withthe vapors of the liquid, thus producing a non-explosive vapor mixture.The compressor 23, which can be one of the liquid piston type or aliquid-driven ejector compressor, is sized to receive vapors at peakrates of loading tank 16. It can be provided with a speed control (notshown) or other means to permit operation at lower than maximum rates'.

The gasoline in reservoir 31 is supplied from the storage tank 10through line 40, said gasoline being pumped by means of pump 41 througha heat exchanger 4 2 which cools the gasoline before it is passedthrough line 43 into said reservoir. A refrigeration unit 50 isconnected with said exchanger and withdraws heat therefrom as therefrigerant is passed through lines 51 and 52. Similarly, coolant fromthe refrigeration unit is passed through lines 53 and 54 into the bodyof cold gasoline in reservoir 31, thereby providing further cooling ofthe gasoline therein. The reserve of cold gasoline in the reservoir iskept at a predetermined level by means of a level control 55 which actsto regulate the flow of gasoline in line 43 by controlling the settingof valve 56 in said line. Generally speaking, pump 41 will operate inmost instances only when pump 33 and compressor 23 are actuated toprocess incoming vapors inasmuch as gasoline is pumped into reservoir 31at about the same rate as it is withdrawn therefrom for passage to thesystem operates independently of the others, it being actuated when thetemperature of the gasoline in reservoir 31 rises above the proper leveleither upon long standing or as a result of introducing fresh gasolineto replace that which is pumped to the compressor and to thecondensation column.

Returning to the processing of the recovered vapors, the effluent fromcompressor 23 passes via line 59 to a lower portion of a condensationcolumn 60 operated under moderately elevated conditions or pressure,e.g., about 25 to 85 psig. On entering said column, the liquid componentof the compressor effluent falls into a pool 71 of gasoline maintainedin the bottom of the column,

'downwardlycascading, refrigerated gasoline stream.

The interrelated conditions of temperature and pressure within column 60are maintained at such levels that vapors exiting from the column to theatmosphere through a vent line 65 will contain less than percent byweight of hydrocarbon or other vapors of the liquid beingloaded; Suchvapor exit occurs as pressures build up above the level to be maintainedin the column, thereby opening a back-pressure or pressure relief valve70 in the vent line. For example, when loading gasoline the method ofthis invention will reduce the hydrocarbon content of the vented streamto a level of approximately 7 percent by weight when the column isoperated at a vapor exit temperature of 10 F. and a pressure of 30 psig.The same result can be obtained by increasing the vapor exit temperatureto 20 F. while maintaining a column pressure of about 60 to 65 psig, orby using a vapor exit temperature of about 30 F.

.and pressures of approximately 80 to 85 psig. The

column is preferably operated at pressures of about 25 to 40 psig and atthe corresponding vapor exit temperatures ranging from about 5 to F.

As indicated above, a pool 71 of gasoline is maintained in the bottom ofcolumn 60, and liquid is continuously withdrawn from this pool throughline 63 for return to the storage tank 10 during loading periods,

when gasoline is enteringthe column through line 61. A liquid levelcontrol 66 maintains this pool at a generally constant level throughactivation of valve 67 in line 63. The unit is preferably sized so thatat peak vapor-receiving rates the temperature of the gasoline leavingthe absorber volume approaches ambient; for example, gasoline which issupplied at the top of the column at l0 F. is warmed to about 60 to 65F.in its passage downwardly through the column. At less than maximumvapor-receiving rates, the flow of gasoline to the top of the absorbercolumn is-cut back by means of a temperature control instrument 68 whichsenses the presence of unduly low temperatures and acts to partiallyclose valve 69 in line 61, thereby cutting down the flow of refrigeratedgasoline as well as effecting any necessary change in the speed of pump33. This reduces the operating costs of the system It has been foundthat by starting with a supply of approximately 3,000 gallons ofgasoline in the cold storage reservoir at 10 F., and by pumpingrefrigerated gasoline therefrom to the condensation column (operated at30 psig) at a rate of 85 gallons per minute (gpm) and to the compressorat a rate of gpm, it is possible to loadtank 16 with gasoline for fiftyminutes at a peak rate of 5,000 gpm while still maintaining thehydrocarbon content of the vapors discharged through vent 65 at a levelof approximately 7 percent by weight. In such an operation, liquid fromcolumn 60 at 60 F. would be discharged through line 63 at a rate ofapproximately ll8 gpm. This reflects an increment of 8 gpm of gasolinerecovered from the vapors as a result of vapor condensation andabsorptiontaking place in column 60. 1

Possible difficulties due .to the formation of ice crystals in theportion of the system subjected to refrigeration can be overcome by theaddition to the gasoline passing through line 40 of an effective amounof an anti-freeze agent.

While this invention has been described in conjunction with preferredembodiments thereof, it is obvious that many modifications and changestherein can be made by those skilled in the art without departing fromthe spirit and scope of this invention as defined by the claims appendedhereto.

Iclaim: l. A method of recovering condensable vapors from a mixture ofcondensable and inert vapors discharged from tanks being loaded with avolatile liquid similar to I the condensable vapors, said methodcomprising (:01-

lecting said mixture of vapors; saturating the collected vapor mixturewith the vapors of said volatile liquid by contacting said mixture witha first refrigerated streamv of said liquid; compressing the saturatedvapor mixture in the presence of said refrigerated stream; contactingthe compressed saturated vapor mixture under elevated pressure in acondensation zone with a second refrigerated stream of the volatileliquid whereby the condensable vapors are takenup by said stream; andrecovering the resulting augmented liquid stream from the condensationzone.

- I 2. The method as recited in claim '1 wherein the liquid being loadedis a hydrocarbon fuel, wherein the temperature of the first and secondrefrigerated streams is about 5 to 15 F, and wherein the pressuremaintained in the condensation zone is about 25 to p'.s.i.g. so as toconvert to liquid at least percent of the hydrocarbon content of thecollected vapors.

3. The method as recited in claim 2 which includes the steps ofmaintaining a reserve of the volatile liquid in a refrigerated conditionand in such volume as to permit vapors to be collected at peaktank-loading rates for an extended period of time.

4. The method as recited in claim 1 wherein the collected vapor mixtureis simultaneously compressed and saturated by passing the same to acompressor along with the first refrigerated stream.

5. The method as recited in claim 4 wherein the liquid stream to thecompressor is a refrigerated one.

6. Apparatus for recovering vapors from a receiving tank into which avolatile liquid is introduced, including means for collecting vaporsdisplaced from the receiving tank, a vapor saturator and saturated vaporcompressor in flow communication from said collecting means,refrigeration means, including a reservoir vessel, for maintaining arefrigerated supply of the volatile liquid in said vessel, a volatileliquid supply tank in flow communication with said receiving tank andsaid reservoir vessel, together with means for flowing the liquid fromthe supply tank into the receiving tank and reservoir vessel, a vaporcondensation column in flow communication from the compressor and fromthe reservoir vessel as well as with the supply tank, said column beingadapted to condense incoming vapors from the compressor by contactingthe same under elevated pressure with incoming refrigerated liquid fromthe reservoir vessel and to discharge liquid introduced into the column,along with the condensate, to the supply tank while venting uncondensedvapors to the atmosphere, and means for flowing refrigerated volatileliquid from the reservoir vessel to the condensation column.

7. The apparatus of claim 6 wherein the reservoir vessel is also in flowcommunication with the compressor and which includes means for flowingrefrigerated volatile liquid from said vessel to the compressor.

1. A method of recovering condensable vapors from a mixture ofcondensable and inert vapors discharged from tanks being loaded with avolatile liquid similar to the condensable vapors, said methodcomprising collecting said mixture of vapors; saturating the collectedvapor mixture with the vapors of said volatile liquid by contacting saidmixture with a first refrigerated stream of said liquid; compressing thesaturated vapor mixture in the presence of said refrigerated stream;contacting the compressed saturated vapor mixture under elevatedpressure in a condensation zone with a second refrigerated stream of thevolatile liquid whereby the condensable vapors are taken up by saidstream; and recovering the resulting augmented liquid stream from thecondensation zone.
 2. The method as recited in claim 1 wherein theliquid being loaded is a hydrocarbon fuel, wherein the temperature ofthe first and second refrigerated streams is about 5* to 15* F, andwherein the pressure maintained in the condensation zone is about 25 to85 p.s.i.g. so as to convert to liquid at least 90 percent of thehydrocarbon content of the collected vapors.
 3. The method as recited inclaim 2 which includes the steps of maintaining a reserve of thevolatile liquid in a refrigerated condition and in such volume as topermit vapors to be collected at peak tank-loading rates for an extendedperiod of time.
 4. The method as recited in claim 1 wherein thecollected vapor mixture is simultaneously compressed and saturated bypassing the same to a compressor along with the first refrigeratedstream.
 5. The method as recited in claim 4 wherein the liquid stream tothe compressor is a refrigerated one.
 6. Apparatus for recovering vaporsfrom a receiving tank into which a volatile liquid is introduced,including means for collecting vapors displaced from the receiving tank,a vapor saturator and saturated vapor compressor in flow communicationfrom said collecting means, refrigeration means, including a reservoirvessel, for maintaining a refrigerated supply of the volatile liquid insaid vessel, a volatile liquid supply tank in flow communication withsaid receiving tank and said reservoir vessel, together with means forflowing the liquid from the supply tank into the receiving tank andreservoir vessel, a vapor condensation column in flow communication fromthe compressor and from the reservoir vessel as well as witH the supplytank, said column being adapted to condense incoming vapors from thecompressor by contacting the same under elevated pressure with incomingrefrigerated liquid from the reservoir vessel and to discharge liquidintroduced into the column, along with the condensate, to the supplytank while venting uncondensed vapors to the atmosphere, and means forflowing refrigerated volatile liquid from the reservoir vessel to thecondensation column.